implement wait tree widget

src/core/hle/kernel/kernel.h

@@ -149,6 +149,9 @@ public:
     /// Wake up all threads waiting on this object
     void WakeupAllWaitingThreads();
 
+    /// Get a const reference to the waiting threads list for debug use
+    const std::vector<SharedPtr<Thread>>& GetWaitingThreads() const;
+
 private:
     /// Threads waiting for this object to become available
     std::vector<SharedPtr<Thread>> waiting_threads;